1. Field of the Invention
The invention relates to an engine stroke discriminating method and apparatus for controlling the ignition timing and/or the fuel injection timing of a 4-cycle internal combustion engine.
2. Description of the Prior Art
In some conventional ignition systems of 4-cycle internal combustion engines, the ignition timing is set in accordance with the rotational angle of the crankshaft. In an ignition system of this type, ignition is produced for every two rotations of the crankshaft during each compression stroke. If a spark is produced at an ignition plug at a predetermined rotational angle of the crankshaft, an additional spark, that is, a waste firing, will occur in the exhaust stroke. In order to prevent such an additional spark, it is necessary to detect or discriminate between the different strokes of the engine. Japanese Patent Publication No. 60-20583 discloses an ignition system wherein a rotational position detecting sensor is provided for a half rotation member such as a camshaft which makes one full rotation for each two crankshaft rotations. An ignition pulse is provided only during a compression stroke in accordance with the result of detection of a predetermined rotational angular position of the half rotation member such as the camshaft. However, since the ignition system requires provision of the rotational position detecting sensor on the half rotation member, there is a problem in that the output portion of the crankshaft is complicated in construction and accordingly has a high production cost. This also applies to an ignition system of an internal combustion engine of the fuel injection type wherein fuel injection timing for injecting fuel once during each one cycle (suction, compression, explosion and exhaust) of the engine is set for each of the cylinders of the engine.